The main thrust of this proposal concerns the use of Xenopus oocytes programmed with synthetic HBV mRNAs to reconstitute de novo the assembly of HBV envelope and virion particles from their individual antigen building blocks. I will determine which antigen-antigen interactions provide the underlying driving force for each phase of the assembly process. Specifically I will address the role of preS1 and preS-2 in the production of filamentous envelope structures and which of the surface envelope components interacts with HBV cores to drive virion formation. I will also investigate the viral antigen requirements for the assembly of HBV cores and for the selective packaging of the HBV pregenome RNA and the inclusion of reverse transcriptase activity. I will also use the oocyte system to reconstitute the transactivation of HIV genetic information that occurs when the viral TAT gene product interacts with a specific transactivation response or TAR element. Specifically, I will try to answer the controversial question of whether TAT acts by translational activation or stabilization of mRNA, or by activation of transcription. This study will also determine the potential of oocytes as an assay system for transactivating factors.